1. Field of the Invention
The invention relates to an electronic image processing system and particularly, but not exclusively, to a system for modifying initial image data to produce data representing a modified image.
2. Description of the Related Art
Electronic image processing systems are known for modifying an initial image to produce a modified image having a different shape, size and/or position as compared to that of the initial image. For example, our British patent application published as GB-A-2,113,950 and corresponding US patent U.S. Pat. No. 4,602,286, the teachings of which are incorporated herein by reference, both disclose a system for performing picture composition. Our British patent application published as GB-A-2,119,594 and corresponding US patent U.S. Pat. No. 4,563,703, the teachings of which are incorporated herein by reference, both disclose a system for producing effects by writing input video signals received in raster order to a store in such an order that the shape, size and/or position of the image is altered. Also, our British patent application published as GB-A-2,158,671, the teachings of which are incorporated herein by reference, discloses a system in which picture data is modified using three-dimensional transformations so that the shape, size and/or position of the image appears to undergo a corresponding change in three dimensional space. Once modified, the three-dimensional signals are converted into two-dimensional signals which represent the image as it would appear if projected onto a viewing screen thereby producing a perspective effect in the modified image. A similar perspective manipulation is disclosed in our European patent application published as EP-A-283,158 and corresponding US patent U.S. Pat. No. 4,951,040, the teachings of which are incorporated herein by reference.
The systems disclosed in the above mentioned patent specifications are directed to the modification of image data at television resolution up to high definition standards e.g. 1250 lines at 50 Hz. As the size or resolution of an image increases there is a corresponding increase in the amount of data that has to be modified in order to achieve a given effect. There is also a corresponding increase in the amount of time taken to process the data, and when manipulating print-quality pictures comprising say 8000.times.10000 picture points the delay is noticeable and unacceptable to the user of the system.
Where there is a change in the perspective of the image, the transformations to be applied to the image data will vary along the height and/or width of the image in order to achieve the effect of foreshortening associated with perspective views. The need to vary the transformations applied to image elements between one element and the next introduces a further level of complexity to the system.